Various types of preamplifier devices have hitherto been proposed for use with MCT detectors.
The conventional MCT detector preamplifiers, however, maintain a fixed current through the MCT detector and measure the voltage generated across the MCT detector. In effect, therefore, the resistance change caused by the illumination or incident light typically is monitored, rather than the change of conductance through the MCT detector. This technique generally has resulted in inherently non-linear output measurements.
Accordingly, a serious disadvantage is presented by the above discussed prior art preamplifiers in order to meet their operational criteria of maintaining a fixed current through the light detector while measuring the voltage generated across it.
The present invention involves a novel approach and circuit features combined in such a way as to afford a substantial solution to the difficulties, problems and generally not precise measurements encountered/tolerated in the prior art.
For example, in total contrast to the prior art, the present invention provides a preamplifier circuit arrangement or network for maintaining a generally fixed voltage across the MCT detector while measuring or detecting a current through the varying incident light.